This invention relates to an apparatus and method for deploying tools in oil wells with mud pumping techniques, and has special application for use in highly deviated wells.
Once an oil well is drilled, it is common to log certain sections of the well with electrical instruments. These instruments are sometimes referred to as "wireline" instruments, as they communicate with the logging unit at the surface of the well through an electrical wire or cable with which they are deployed. In vertical wells, often the instruments are simply lowered down the well on the logging cable. In horizontal or highly deviated wells, however, gravity is frequently insufficient to move the instruments to the depths to be logged. In these situations, it is sometimes necessary to push the instruments along the well with drill pipe.
Wireline logging with drill pipe can be difficult, however, because of the presence of the cable. It is cumbersome and dangerous to pre-string the electrical cable through all of the drill pipe before lowering the instruments into the well. Some deployment systems have therefore been developed, such as Schlumberger's Tough Logging Conditions System (TLCS), that make the electrical connection between the instruments and the cable down hole, after the instruments have been lowered to depth. In these systems, the electrical instruments are easily deployed with standard drill pipe, and the cable is then run down the inside of the drill pipe and connected. After logging, the cable can be easily detached from the logging tool and removed before the tool is retrieved. The TLCS has been very effective and has achieved strong commercial acceptance.
In the TLCS and other systems, the cable is remotely connected to the instrumentation with a down hole connector. One half portion of this connector is attached to the instrumentation and lowered into the well on drill pipe. The other half portion of the connector is attached to the end of the cable and pumped down the drill pipe with a flow of mud that circulates out of open holes at the bottom of the drill pipe and into the well bore. The connector is sometimes referred to as a "wet connector" because the connection is made in the flow of drilling mud under conditions that challenge electrical connection reliability. In highly deviated or horizontal wells, pumping the connector down the well can be especially challenging. In such cases the pumping force exerted on the connector must overcome friction between the well casing or drill pipe surface, and in some instances must even act against gravity.
The challenge of pumping the cable connector down the well applies to pumping any wireline tool down a well with a flow of drilling muds, which can, depending on the application and down hole environment, have a wide range of weights and viscosities.